How is desulfurization carried out in circulating fluidized bed boilers?
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How is desulfurization carried out in circulating fluidized bed boilers?
There are many desulfurization methods: in-furnace desulfurization and out-of-furnace desulfurization
Desulfurization: Typical circulating fluidized bed boilers operate at temperatures of 850–900°C. At these temperatures, limestone can undergo complete calcination, with calcium carbonate being converted into calcium oxide. Calcium oxide then reacts with sulfur dioxide produced by coal combustion to form calcium sulfate, which is discharged in solid form, thereby achieving desulfurization. Limestone calcination reaction equation: CaCO3 → CaO + CO2 + heat Q. Desulfurization reaction equation: CaO + SO2 + 1/2O2 → CaSO4 + heat Q. Therefore, circulating fluidized bed boilers enable efficient and cost-effective desulfurization within the furnace, with a desulfurization rate of generally over 90%.
One advantage of the circulating fluidized bed is its ability to enable simple and efficient desulfurization within the furnace; limestone particles can be added at locations such as the secondary air ducts and the return leg, in accordance with the designed calcium-sulfur ratio!
Flue gas desulfurization still relies mainly on processes carried out outside the furnace: the initial methods such as the ammonia method, limestone-gypsum method, and double-alkali method – nowadays only the limestone-gypsum method is widely used; the other methods present difficulties in terms of equipment corrosion, treatment of by-products, site hygiene, and desulfurization efficiency； In addition, desulfurization inside the furnace has many disadvantages: slag tends to form at the bottom of the furnace, fly ash tends to clump together, and the quality of the ash and slag deteriorates, making them difficult to handle. Based on personal experience, for reference only ；
This is only in-situ desulfurization, and a large amount of lime is required; compared to the wet desulfurization method using lime slurry outside the furnace, its cost is 30%-50% higher. The choice depends on actual needs – if operation is continuous, external desulfurization is recommended, while for intermittent operation, in-situ desulfurization will suffice